In prior art floatation machines the process of separating froth concentrate from gangue involves either froth floatation at which the source feed is pulp containing small fractions of a material to be concentrated or a combination of froth floatation and froth separation at which the source feed contains both small fractions of a material to be separated and a large fraction thereof supplied to the froth layer. The techniques involving froth floatation and a combination of froth floatation and froth separation are characterized by the need to maintain a predetermined pulp level in the chamber of a floatation machine relative to its overflow threshold, thereby keeping the froth layer thickness and the pulp-froth interface within required limits; to ensure a predetermined ratio between liquid and gaseous phases in the pulp supplied to the chamber of a floatation machine, the density and level of the pulp in the chamber being primarily determined by said ratio; to maintain optimal concentration in the aerated pulp of frother supplied both with circulating water and directly with the source feed, which determines the size, degree of dispersion and the lifting speed of air bubbles and, consequently, the density of the aerated pulp; to provide an optimal speed of supplying the source feed to the bulk of the aerated pulp in the chamber of a floatation machine, variations of said speed adversely affecting flow hydrodynamics; to discharge gangue from the chamber with minimum losses of the pulp liquid phase; and to rapidly restore the pulp level and density in the chamber to preset values.
Variations of the pulp level and, consequently, of the froth layer and also of the ratio between the solid, liquid and gaseous phases of the pulp are attributable, firstly, to changes in the quantity of the source solid and water in the chamber of a floatation machine and, secondly, to changes in liquid phase losses when gangue is discharged due to a varying amount of the solid and large and heavy fractions thereof. Variations of the pulp level in the chamber of a floatation machine are also attributable to changes in the pulp density due to a varying concentration of frother in the pulp.
A change in the speed of supplying the pulp to the chamber of a floatation machine is caused by a variation of the solid--water ratio in the pulp. Thus, the disturbing factors affecting the process of froth floatation include changes in the quantity of the solid and liquid phases of the pulp fed to the chamber of a floatation machine, changes in the quantity of the liquid phase lost in discharging the gangue due to a varying content of large and heavy fractions therein, and changes in the concentration of frother in circulating water supplied to the chamber, which cause variations of the liquid and gaseous phases in the pulp and, consequently, of the pulp level and density in the chamber of a floatation machine.
From the aforesaid it follows that, at the present time, a vital problem in the art is quality regulation of the processes of froth floatation and froth separation combined with froth floatation, which involves related adjustment of several parameters. This problem is particularly acute with large-capacity floatation machines due to great sluggishness of a floatation installation comprising such machines and also due to the presence of powerful disturbing factors which are widely different.
The above problem is partially solved in a known device for automatic regulation of the process of separating froth concentrate from gangue in a floatation machine (cf. G. M. Kovin et al. "Systemy avtomaticheskogo kontrolya i upravlenia tekhnologicheskimi protsessami flotatsionnykh ustanovok". Moscow, "Nedra" Publishers, 1981, pp. 69-73), comprising a pulp level measuring circuit wherein a bubbling pipe located in the chamber of the floatation machine communicates with a pressure pickup and with an air flow regulator. The output of the pressure pickup is connected to a pulp level recorder and to the input of a circuit designed to regulate the rate of discharging gangue from the chamber of the floatation machine, the output of said circuit being connected to the drive of a control valve installed on a branch pipe used to discharge gangue from the chamber of the floatation machine. The foregoing device also includes a frother flow-rate regulating circuit wherein the rate of frother flow is regulated in proportion to the flow of gangue discharged from the chamber as pulp.
Such an automatic regulator device does not provide for required regulation quality due to the fact that, during measurements of the pulp level in the chamber of the floatation machine, no account is taken of the error associated with pulp density variations.
If no pulp density monitoring means are provided, frother metering with respect to the flow rate of gangue discharged as pulp is very approximate and upsets the processes of froth formation and hydrodynamics in the chamber due to considerable variations of the pulp density, which hinders the process of pulp level stabilization. Furthermore, the absence of such a regulating factor as stabilization of the flow rate of water containing frother during floatation impairs the pulp density.
Thus, the foregoing automatic regulator device does not provide for required regulation quality, particularly with large-capacity floatation machines due to the influence of powerful disturbing factors and great sluggishness of floatation installations utilizing such machines.
The above problem is partially solved in another known device for automatic regulation of the process of separating froth concentrate from gangue in a floatation machine (cf. GB, A, 2180779), comprising a channel for measuring a pulp level and density in the chamber of the floatation machine, in which two bubbling pipes installed at different levels in the bulk of the pulp in the chamber of the floatation machine are in communication with air flow regulators and a differential pressure pickup connected to the input of a channel designed to regulate the flow rate of frother supplied to the chamber of the floatation machine and to one data input of a pulp level correction unit whose other data input is connected tea pressure pickup communicating with one of the bubbling pipes, while the output of said pulp level correction unit is connected to the input of a channel used for stabilizing the pulp level in the chamber of the floatation machine and incorporating a circuit designed to regulate the rate of discharging gangue from the chamber of the floatation machine and connected to a gangue-discharge control valve installed on a branch pipe adapted to discharge gangue from the chamber of the floatation machine.
Similarly to the previously mentioned device, the last described automatic regulator device does net provide for required regulation quality, a disadvantage associated with the fact that stabilization of the pulp level solely by changing the rate of gangue discharge from the chamber of a floatation machine is generally ineffective, particularly with large-capacity floatation machines due to great sluggishness of a floatation installation comprising such a machine and also due to the presence of strong disturbing effects and an insufficient regulating action to rapidly restore the pulp level to a preset value. A mere increase in the gain of the pulp level stabilizing channel at a high level of disturbances will result in system driving, overcontrol and an excessive regulation time whereby regulation quality will be appreciably impaired. The utilization of a more powerful control valve in discharging gangue from the chamber of a highly efficient floatation machine increases its own sluggishness and, as a result, the sluggishness of the floatation installation comprising automatic means in addition to the floatation machine and impairs regulation quality.
In the disclosed automatic regulator device, the rate of gangue discharge from the chamber of the floatation machine can be changed by the use of a control valve having a nonlinear flow characteristic, a feature making it impossible to obtain required regulation quality. Such a control valve does not provide for the maximum free discharge of gangue from the chamber of the floatation machine with minimum losses of the pulp liquid phase, which gives rise to pulp level disturbances in the chamber of the floatation machine. A vertical position of the afore-mentioned control valve (with the seat of a shut-off valve located horizontally) may cause complete or partial pressing-in of the branch pipe used to discharge gangue from the chamber of the floatation machine in floatation of ore containing a great number of large and heavy fractions. Consequently, the gangue discharge rate will change (decrease) and there will occur additional pulp level disturbances in the chamber of the floatation machine, a factor further decreasing regulation quality.
In its operation, the floatation machine uses circulating water with a residual concentration of frother amounting to 70-80% of its working concentration. The rate of water flow changes as the source feed is supplied to the chamber of the floatation machine and losses occur in discharging gangue from the chamber of the floatation machine. This causes changes in the pulp level and density and also in flow hydrodynamics in the chamber of the floatation machine. Hence, maintaining the working concentration of frother in the pulp in the chamber of the floatation machine solely by changing the additional supply of frother to the chamber of the floatation machine without stabilizing the flow rate of water containing frother will fail to provide, on the one hand, adequate stabilization of water-air ratios in the bulk of aerated pulp and, consequently, of the pulp level and density and, on the other hand, a stable speed of supplying the source feed to the chamber of the floatation machine and, in effect, stable pulp flow hydrodynamics in the chamber of the floatation machine.